1. Field of the Invention
The present invention relates to well tools for selectively plugging tubing strings extending within a well bore and to hydraulically-operated well bore devices, such as well packers, to permit pressure buildup therein necessary for operating such devices, and to a method for subsequently opening such tubing strings and devices.
2. Description of the Prior Art
While drilling and producing wells for the recovery of petroleum and other subsurface deposits, it is often necessary to close off or plug a tubular conduit, such as a string of tubing extending from the well surface to a subterranean location, at a chosen point along the length of conduit so that pressure may be built up within the conduit above that point. Subsequently, it is necessary to be able to re-open the conduit for flow therethrough. For example, it may be necessary to pack-off the annulus between the tubing and a surrounding casing or well bore. This is typically done with a packer which is made up into and forms a part of the tubing string. Many such packers are set hydraulically by application of fluid pressure through the tubing. A plug apparatus is used to permit sufficient pressure to be built up within the tubing string to set the packer. Such packers are typically designed so that once set, they may be held or retained in the set condition without the continued application of fluid pressure through the tubing. Thus, the plug used to close off the tubing during setting of the packer may then be released so that fluid may be circulated through the tubing.
Flow control devices of the type under consideration also have applicability and utility in situations prior to formation perforation. For example, it may be desirable to create an underbalance adjacent the formation to be produced so that when the formation is perforated, flow is immediately initiated into the tubing, avoiding potential fouling of the newly created flow paths into the formation.
A variety of bridging and blanking plugs are shown in the prior art for plugging off the bore of a well conduit, usually the production tubing string, for various purposes. Although certain of these plugs are designed to be permanently installed, they are usually of the type which are designed to be retrieved when the purpose for which the plug has been installed has been accomplished. Retrievable plugs generally employ some form of releasable anchoring device by which the plug may be secured to the internal bore of the well pipe and which may then be released to enable the plug to be withdrawn. Typically, a seating nipple is made up in the tubing string which includes an internal profile adapted to receive locating collets, or the like, on the plug body. Typical seating nipples are shown, for example, on pages 28-36 of the Baker Oil Tools 1989 Flow Control Systems catalogue. Seating nipples of the type shown allow, for example, the location of various wireline flow control devices within the internal bore of a tubing string.
One disadvantage of the prior art arrangement was that the seating nipple presented a restriction in the internal diameter of the tubing string. Also, the prior art plugs were often retrieved on a wireline and the retrieval operation was complicated in the case of deviated well bores.